"We've almost completed that task [of defeating ISIL] and we'll be making a determination very quickly, in coordination with others in the area, as to what we'll do," said Trump on Tuesday during a White House press conference with leaders from three Baltic nations.

"Saudi Arabia is very interested in our decision, and I said, 'Well, you know, you want us to stay, maybe you're going to have to pay'."

Trump spoke on Monday with the King of Saudi Arabia, Salman bin Abdulaziz Al Saud, over the phone to discuss a range of regional issues, including a peace plan between Israelis and Palestinians and opportunities to strengthen the American-Saudi strategic partnership.

But the White House statement of the call, released on Tuesday, did not mention any discussion about Saudi Arabia's boosting funding for US military efforts in Syria.

Similarly, a White House readout of his March 20 meeting with Saudi Crown Prince Mohammed Bin Salman made no mention of US military efforts in the region.

'I want to get out'

Trump's remarks appeared to contradict the rhetoric on Syria from other top US officials. Defense Secretary Jim Mattis and former Secretary of State Rex Tillerson had pledged an enduring presence in Syria last year.

But Trump reiterated calls to end US presence in the region, after he made similar statements at an event in Ohio last week.

"I want to get out. I want to bring our troops back home," Trump said.

"We do a lot of things in this country, we do them for a lot of reasons, but it is very costly for our country, and it helps other countries a hell of a lot more than it helps us," he added.

Trump also railed against ongoing US intervention in the Middle East and its growing cost.

"Think of it, $7 trillion over a 17-year period. We have nothing. Nothing except death and destruction. It's a horrible thing. So it is time. It is time," he said at the White House press conference.

"We were very successful against ISIL. We'll be successful against anybody militarily. But sometimes it is time to come back home. And we're thinking about that very seriously."

The Obama administration launched a war in 2014 against the ISIL after the group flourished in the chaos of the Syrian civil war and then surged over the Iraq border in a bid to overtake Baghdad.